The present invention relates in a general manner to interbody cages intended to partially or completely replace an intervertebral disc in surgical treatment of the spine and to permit bone fusion between the overlying and underlying vertebral plates.
A number of types of interbody cages are already known in the prior art. One cage which is particularly widely used is made up of a one-piece body made of biocompatible material such as a titanium alloy or a stainless steel, of which the upper surface and the lower surface have reliefs such as serrations of triangular cross section which are intended to provide anchoring in the overlying and underlying vertebral plates when the distraction effected between the vertebrae for the purpose of fitting the implant is released. Such a cage is also provided with at least one opening which passes through the body from top to bottom and opens out on its upper and lower faces. The cavity constituted by this opening is filled with an osteogenic material or bone graft so as to ensure bone growth through it between the vertebral plates and, in the long term, rigid bone fusion between these plates.
However, these known cages have certain limitations, particularly in terms of the stability of the anchoring in the vertebral plates over time, which stability is essential in order to achieve bone fusion.
These cages are also poorly adapted to the cervical vertebrae, where the incurved configuration of the vertebral plates can render the principle of this anchoring by serrations insufficient per se.
The present invention aims to overcome these limitations of the prior art and to propose a novel implant of the interbody cage type which is well adapted to implantation in the region of the cervical vertebrae and which is able to be joined to the vertebral plates with an excellent quality of anchoring.
Another object of the invention is to propose an implant of the interbody cage type whose fitting is particularly simple and whose weight can be reduced compared with the entirely metal cages of the prior art, and whose manufacture can therefore be made simpler and less expensive.
Thus, the invention proposes an implant of the interbody cage type, particularly for cervical vertebrae, comprising a body which has an upper face and a lower face, which are able to bear on the overlying and underlying vertebral plates, and which also comprises at least one through-opening which opens out on the said upper and lower faces, characterized in that it additionally comprises an anchoring member mounted in such a way as to be able to move in the said opening, the said anchoring member comprising a bearing part adjacent to a first vertebral plate, and at least one projecting anchoring element extending from the said bearing part in the direction of the opposite vertebral plate, such that when the implant is compressed between the vertebral plates, the said anchoring member is stressed by the first vertebral plate in the area of the said bearing part so as to move in relation to the body and so that the said projecting element at least provided juts out from that face of the body turned toward the opposite vertebral plate and anchors in the latter.
Preferred but nonlimiting features of the implant according to the invention are as follows:
the body has, on at least one of its upper and lower faces, complementary anchoring arrangements,
the said anchoring member has a plurality of projecting elements,
the said projecting elements are elongate and essentially parallel to one another,
the projecting anchoring element or each projecting anchoring element has the form of a rod with a pointed free end,
the said opening of the body has a bearing arrangement for the said anchoring member in order to limit the course of movement of the latter caused by the said first vertebral plate,
the said arrangement consists of a shoulder between two parts of different sizes of the said opening,
the said bearing part of the anchoring member fits tightly into the larger-sized part of the said opening,
when the anchoring member bears against the bearing arrangement, the bearing part of the said member is entirely inscribed within the lower face of the body,
the anchoring member has a plurality of projecting anchoring elements all fitting tightly into the smaller-sized part of the said opening,
the said bearing part of the anchoring member has the form of a ring in which a central opening ensures continuity of passage between the upper and lower faces of the body, through the said opening of the body,
the body has a generally rounded external form, with zones of greater curvature and zones of lesser curvature,
the said opening of the body has a contour with a form similar to the said outer form of the body,
the anchoring member is provided with a plurality of projecting elements situated in the vicinity of zones of greater curvature of the said opening and received in recesses formed in these zones,
one of the upper and lower faces of the body is convex,
the bearing part of the anchoring member is generally plane,
the body is made of a biocompatible polymer material such as polyetherether ketone,
the anchoring member is made of a biocompatible metal alloy.
Other features, aims and advantages of the present invention will become clearer on reading the following detailed description of a preferred embodiment thereof, given as a nonlimiting example and with reference to the attached drawings, in which:
FIG. 1 is a perspective view of an implant according to the invention,
FIG. 2 is a front elevation view of the implant in FIG. 1,
FIG. 3 is a bottom view of the implant in FIGS. 1 and 2,
FIG. 4 is a top view of the implant in FIGS. 1 to 3,
FIG. 5 is a longitudinal sectional view along the line Vxe2x80x94V in FIG. 4,
FIG. 6 is a transverse sectional view along the line VIxe2x80x94VI in FIG. 4, in a first position of the implant, and
FIG. 7 is a view analogous to FIG. 6, in a second position of the implant.